Work on techniques for detecting the position at which a user is gazing by detecting the direction in which the user is gazing has been proceeding for many years. As one example of such techniques, there is proposed a technique in which an image captured of the user's eye is analyzed to detect the user's pupil and a corneal reflection image of a light source and, based on the displacement between the position of the corneal reflection image and the position of the pupil, the user's gaze is detected (for example, refer to Japanese Laid-open Patent Publication Nos. 2012-65719 and 2012-115505). The corneal reflection image of the light source is referred to as the Purkinje or Purkyne image. In the present application, the corneal reflection image of the light source will be referred to as the Purkinje image.
The technique that uses the Purkinje image for gaze detection requires that the Purkinje image be detected accurately. However, if the separation distance between the light source illuminating the user's eye and the camera used to capture an image of the user's eye is small, the light from the light source is reflected by the user's retina, and the reflected light passed through the user's pupil reaches the camera. It is known that this can result in a bright pupil phenomenon in which the entire pupil appears bright on the image captured by the camera. If this happens, the Purkinje image may become difficult to detect, because the contour of the Purkinje image becomes unclear.